The present invention relates to an electronic circuit for generating a stable reference voltage. More particularly, the invention involves a refined bandgap type reference circuit which incorporates a temperature and process variable insensitive start-up circuit and has the capability to operate in a power-down mode.
Bandgap type reference voltage generating circuits have recently become popular for providing precise reference voltages on integrated circuit devices. The article entitled "A Precision Curvature-Compensated CMOS Bandgap Reference" by Song et al. which appeared in the IEEE Journal of Solid-State Circuits, December 1983, pp. 634-643, and the article entitled "A Precision CMOS Bandgap Reference" by Michejda et al. which appeared in the IEEE Journal of Solid State Circuits, December 1984, pp. 1014-1021, are examples of the relatively recent analyses and design efforts expended to develop bandgap reference circuits which are stable over extended temperature ranges. A further variation of related work is set forth in U.S. Pat. No. 4,588,941. The focus of these developments was to eliminate bandgap reference voltage variations attributable directly to temperature. Neither start-up problems nor power-down capabilities were meaningfully addressed in the references.
Start-up circuits per se are known. For example, U.S. Pat. No. 3,648,154 discloses a circuit for starting a diode string reference used in conjunction with a bipolar differential amplifier circuit. A simple bandgap start-up circuit does appear in U.S. Pat. No. 4,618,816, but as configured remains as an active element affecting the reference regulation loop after start-up. The general concept of powering down a reference circuit is described in U.S. Pat. No. 4,419,594, wherein the power-down transistors are selectively located in the circuit to disable the reference circuit.
In the presence of such teaching, there remains the need for a bandgap voltage reference generating circuit which provides a stable output voltage with temperature, includes a temperature insensitive start-up capability, completely decouples the start-up circuit effects during steady-state reference voltage generation, and incorporates an effective power-down capability. Foremost, these objectives must be met in a commercial environment where daily process variations do not materially degrade operability of the circuit. It is combinations of these features that the present invention addresses.